Muhammad bin Abbad bin Ja'far (may Allah have mercy on him) said that Sayyiduna Ibn Umar (may Allah be pleased with them both) bought something, and the seller scooped it into the measure for him with his hands. Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: Let go with your hand and do not hold it over its top, for I am only entitled to what the mikyal (measuring vessel) takes.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11157